1. Field of the Invention
The present invention relates to a bearing unit for supporting a wheel axle of a railway carriage via a roller bearing.
2. Description of the Related Art
A bearing unit for a railway carriage wheel axle is generally provided with a roller bearing to be mounted on the wheel axle, and a pair (front and rear) of ring members mounted on the wheel axle for axial positioning of an inner race of the roller bearing. One of the ring members serves as a rear cover butted to rear end face of the inner race, and the other as an oil thrower butted to a front end face thereof, or as a rear cover and a front cover butted to the respective end faces thereof, and both are constituted of a heat-treated carbon steel.
FIG. 5 is a cross-sectional view of an ordinary bearing unit for a railway carriage wheel axle. The bearing unit includes a pair of ring members, namely a rear cover 11 and an oil thrower 12 at the respective end portions of an inner race 3 of a roller bearing 2 mounted on a wheel axle 1. The roller bearing 2 is for example a double-race tapered roller bearing, and includes a split type inner race 3, a one-piece outer race 4, rollers 5 aligned in two rows between the inner race 3 and the outer race 4, and a retainer 6 for the rollers. The rear cover 11 is first insert-fitted to the wheel axle 1, then the roller bearing 2 is mounted and finally the oil thrower 12 is insert-fitted. The oil thrower 12 is pressed against the front end face of the inner race 3, and thereby pressing the rear end face against the front end face of the rear cover 11, thus delimiting an axial position of the inner race 3 with respect to the wheel axle 1. On the respective outer circumferential surface of the rear cover 11 and the oil thrower 12 an oil seal 14, 14 is disposed in sliding-contact therewith, and each oil seal 14, 14 is attached to a seal case 15, 15 extended from a front and rear end portions of the outer race 4.
With respect to such a bearing unit, an excessive radial load, which is characteristic to railway carriages, imposed on the wheel axle 1 applies an excessive bending moment thereto, thus repeatedly applying a stress to a contact interface X between the inner race 3 and the rear cover 11, as well as to a contact interface Y between the inner race 3 and the oil thrower 12. As a result, fretting (wear) is incurred on the contact interfaces X, Y, which produces minute worn powder of the carbon steel. Such fretting wear is inevitable to railway carriages since the wheel axle 1 suffers an excessive radial load, and when the fretting progresses further the positioning accuracy of the bearing unit 2 is degraded, which incurs intrusion of the worn powder into an internal area of the bearing unit 2, and hence deterioration of a lubricant provided therein, thus resulting in shortening a life span of the bearing unit 2.
As an example of a remedy to prevent emergence of such worn powder from fretting, JP-A Laid Open No.2001-027254 discloses a bearing unit provided with a spacer (plate) of a soft material, interposed between the inner race and the ring member such as the rear cover. FIG. 6 depicts a spacer 32 constituted of a soft metal plate or a resin plate interposed at the contact interface X between the inner race 3 and the rear cover 11, so as to keep the inner race 3 and the rear cover 11 from directly colliding with each other, thus to prevent the fretting wear. The spacer is to be replaced when worn out, to thereby prolong a life span of the bearing unit.
Another solution is proposed by JP-A Laid Open No.2001-354136, which provides a bearing unit that prevents intrusion of the worn powder produced by wear due to the direct contact of the inner race and the ring member, into an internal area of the bearing. FIG. 7 depicts an elastic member 33 such as a rubber ring elastically pressed to an outer circumferential surface of the contact interface X between the inner race 3 and the rear cover 11, to prevent leakage of the worn powder from the contact interface X. In this case, the outer circumferential surface of the contact interface is constituted of those of the inner race 3 and the rear cover 11 processed to have a same outer diameter, and butted to each other. The elastic member 33 is firmly pressed against such outer circumferential surface, so as to seal the contact interface X both liquid-tightly and air-tightly, thus to prevent leakage of the worn powder to the bearing unit 2.
The bearing unit for a railway carriage wheel axle shown in FIG. 6 is effective in that the spacer 32 prevents the wear of the inner race 3 and the rear cover 11 and hence reduces the emergence of worn powder, however when a trace amount of worn powder is accumulated, it is inevitable that the worn powder intrudes into an internal area of the bearing, which leads to deterioration of the lubricant. Therefore, this method does not completely solve the problem.
With respect to the bearing unit shown in FIG. 7, though the elastic member 33 can prevent leakage of the worn powder out of the contact interface X between the inner race 3 and the rear cover 11, the original problem of the emergence of the worn powder and the accumulation thereof remain unsettled.
It could be an option to apply the spacer of FIG. 6 and the elastic member of FIG. 7 in combination to a bearing unit, however in this case an increase in the number of components as well as in the number of assembly steps is inevitable, and manufacturing process of the bearing unit becomes more complicated.
Accordingly, it is an object of the present invention to provide a bearing unit for a railway carriage wheel axle that suppresses emergence of the fretting worn powder, and inhibits intrusion of the worn powder into an internal area of the bearing, to thereby simplify the assembly process thereof.